1-Ethyl 4-(2-oxopropyl) 2-(1,2,3,4-Tetrahydro-1,3-dimethyl-2,4-dioxopyrimidin-5-yl)butanedioate

The diester 2 was prepared by the addition of 2-hydroxyacetone to 1 according to the reported procedure [1].

2-Hydroxyacetone (0.2 ml, 2.9 mmol) was added to a solution of 1 (293 mg, 1 mmol) in CH₂Cl₂ (5 ml). The mixture was left at r.t. for 2 h and and filtered through a pad of silica gel (EtOAc) afforded the title compound 2, a colourless oil: 320 mg (94 %).

IR (neat): 3070m, 1725vs, 1700vs, 1660vs, 1640vs, 1483s, 1460s, 1435s, 1375s, 1350s, 1275s, 1250s, 1190s, 1155s, 1090s, 1020s, 780s, 755s.

¹H-NMR (CDCl₃): 7.30 (s, 1H, H-6′); 5.66 (s, 2H, CO₂CH₂COCH₃); 4.16 (q, J = 7.1, 2H, CO₂CH₂Me), 3.88 (dd, J = 8.2, 5.7, H-2); 3.41 (s, Me-1′); 3.32 (s, Me-3′); 3.18 (dd, J = 16.8, 5.7, 1H, H-3); 2.92 (dd, J = 16.8, 8.2, 1H, H-3); 2.13 (s, 3H, CO₂CH₂COCH₃); 1.23 (t, J = 7.1, CO₂CH₂CH₃).

¹³C-NMR (CDCl₃): 207.5 (CO₂CH₂COCH₃), 173.4 (CO₂CH₂COCH₃), 171.3 (CO₂CH₂Me), 162.0 (C-4′), 151.0 (C-2′), 141.7 (C-6′), 109.7 (C-5′), 67.9 (CO₂CH₂COCH₃), 60.8 (CO₂CH₂Me), 39.5 (C-2), 36.5 (Me-3′), 34.2 (C-3), 27.3 (Me-1′), 24.7 (CO₂CH₂COCH₃), (CO₂C(CH₃)₃), 13.4 (CO₂CH₂CH₃).

EI-MS: 340 (M⁺, 4), 295 (4), 294 (10), 267 (5), 266 (13), 239 (2), 238 (8), 237 (6), 194 (12), 193 (100), 169 (2), 167 (5), 166 (13), 165 (11), 110 (2), 81 (15), 80 (8), 69 (2), 68 (4), 56 (2).

Acknowledgment: We thank the Swiss National Foundation for financial support.